1. Field of Invention
The invention is related to a battery module and a method for determining battery module ID and temperature thereof, more particularly, to a battery module for a portable electronic device.
2. Description of Related Art
A battery module can provide energy for operating portable electronic devices (such as mobile phone, person digital assistant, etc.). Every battery module needs to be charged when the power within it is almost run out. However, before a charging operation, a battery type of the battery module should be determined so as to provide an appropriate charging current and voltage according to the specification of the battery module. Temperature is also an important criterion for determining the charging current and voltage. For example, if the temperature of the battery module is too high, the charging current should be reduced or turned off to ensure the battery used in a safe environment.
For acquiring signals related to battery types and temperatures of different battery modules and determining charging states, three or four electrodes positioned on the battery modules are implemented. However, comparing with the four electrodes, battery modules with the three electrodes have an advantage of lowering cost and size.
FIG. 1 is a schematic graph of a conventional battery module. The battery module 10 includes a battery 11, a negative temperature coefficient thermistor NTC1, resistors R1 and R2, and electrodes 12, 13 and 14. The anode of the battery is connected to the electrode 14, and the cathode is connected to the electrode 12. The resistor R1 is serially connected to the resistor R2, and the resistors R1 and R2 are separately connected to the electrodes 12 and 13. Also, the thermistor NTC1 is parallelly connected to the resistor R2. A voltage or current is applied to the electrode 13, and a signal is measured on the electrode 13. The signal is determined with an equivalent resistance of the thermistor NTC1, the resistors R1 and R2. With the signal, the battery type and temperature of the battery module 10 are determined.
FIG. 2a is schematic graph showing resistance ranges of different conventional battery modules. In a first battery module type, the resistances of the resistors R1 and R2 are respectively selected as R1′ and R2′, and the equivalent resistance of the thermistor NTC1, and the resistors R1 and R2 fall in the range between R1′ and R1′+R2′. Also, in a second type of battery module, the resistances of the resistors R1 and R2 are respectively selected as R1″ and R2″, and the equivalent resistance falls in a range of R1″˜R1″+R2″.
Accordingly, when the equivalent resistance is in the range of R1′˜R1′+R2′, the battery module will be classified as the first type and the temperature of which is also acquired, thus the battery is charged according to the charging specification of the first type of battery module. Similarly, when the equivalent resistance is in the range of R1″˜R1″+R2″, the corresponding battery will be classified as the second type and the temperature of which is also acquired, thus the battery is charged according to the charging specification of the second type of battery module.
FIG. 2b is another schematic graph showing resistance ranges of different conventional battery modules. Please refer to FIG. 1 and FIG. 2b. If the equivalent resistances of two types of battery module partially overlap with each other, as illustrated in the range between R1′ and R1″+R2″, and the equivalent resistance measured falls in the range between R1′ and R1″+R2″(such as the shadow in the FIG. 2b), it is hard to determine the battery type and temperature of the battery module. Thus, charging the battery module with an appropriate current and voltage is also impossible. To prevent such overlaps, ranges of equivalent resistances of different battery types of battery modules must be shortened, but the shortened ranges reduce the accuracy for determining the temperature of the battery.
Therefore, a new battery module and charging device should be provided to solve aforesaid problem and would have the ability to modulate the charging current and voltage in accordance with the battery type and temperature of the battery module.